1. Field of the Invention
The present invention relates to an apparatus for fabricating a pre-press, i.e., a preprinting, masking film and, more specifically, to an apparatus for fabricating a masking film employed when different images are to be exposed on different portions of a photosensitive film or the like.
2. Description of the Background Art
In some steps of the pre-press process, a positive film is required on which designated characters or photographs of designated sizes are arranged at designated positions. An outline of a manual pre-press process will be described below with reference to FIG. 1. FIG. 1 shows the steps for providing a positive film 3. A plurality of film negatives a and b are fixed on the desired positions of a transparent film 1a such as a polyester film by means of transparent tapes. In the similar manner, a film negative c is fixed on a transparent film 1b. In the example shown in FIG. 1, the images b and c must be arranged in contact with each other on the positive film in a so-called "hairline register" manner (with no space therebetween). For this purpose, the film negatives b and c are applied on separate transparent films.
Colorless transparent portions r, s and t are formed in mask films 2a and 2b, which are peel-off films comprising a colorless transparent film and a color-dyed transparent film such as a red transparent film overlapping each other, by means of an apparatus for fabricating a pre-press masking film (an automatic plotter with a cutter attached on a head thereof). The colorless transparent portions r, s and t are formed by cutting and peeling off those portions of the color-dyed transparent films which corresponds to trimming frames of the images a, b and c. The colorless transparent portions r, s and t are formed to be a little smaller than the film negatives a, b and c.
The transparent film 1a is laid over with the mask film 2a such that the colorless transparent portions r and s are registered with the film negatives a and b. The transparent film 1is laid over with the mask film 2b such that the colorless transparent portion t is registered with the film negative c. The exposure of the photosensitive film is carried out twice using these two sets of overlapped films. Consequently, a positive film 3 is provided on which the images a.sub.0, b.sub.0 and c.sub.0 are arranged at desired positions. The above described steps are carried out for respective color printing plates of yellow (Y), magenta (M) cyan (C) and black (K) for multicolor printing.
The steps for correcting the positive film 3 will be described in the following. In this example, the image b.sub.0 on the positive film 3 is replaced with another image. First, the film negative b is removed from the transparent film 1a. A new film negative b' (not shown) is fixed by means of transparent tapes or the like at that position at which the film negative was fixed. The mask film 2a provided for the film negative b can be used as the mask for the new film negative b'. By carrying out the same steps as described above, a corrected positive film is provided.
Recently, a layout system employing image processing technology of computers has been incorporated in the pre-press process to replace the manual process. The outline of the layout system will be described with reference to FIG. 2. As shown in FIG. 2, respective images of photographs A, B and C are read by a scanner 4. The read image data are inputted to the layout system 5. Coordinate data for designating trimming frames of the respective images A.sub.0, B.sub.0 and C.sub.0 of the photographs A, B and C are inputted into the layout system 5 in advance by means of a digitizer or the like. The layout system 5 arranges the respective images A.sub.0, B.sub.0 and C.sub.0 of the photographs A, B and C read from the scanner 4 at the desired positions in accordance with the coordinate data. The arranged images are printed on one negative film 6 for each of respective color printing plates through a scanner output portion 5a. The negative film 6 is printed to be solid except for portions of the images A.sub.0, B.sub.0 and C.sub.0 No mask film is used in obtaining the negative film 6.
There are various methods for correcting the negative film 6. Some of the correcting methods will be described with reference to a case in which the image B.sub.0 of the photographs B out of the three photographs A, B and C is replaced with another image of another photograph.
In a first method, a new photograph is set instead of the photograph B to be read by the scanner. A corrected negative film is obtained by using the scanner 4, the layout system 5 and the scanner output portion 5a in a manner similar as in the case of the photograph B. However, in this method, the same steps must be carried out twice. Therefore, it requires much time to provide the corrected film. Such repetition is not desired from the point of view of obtaining the most use of the layout system 5. p In view of the foregoing, another method has been used. In this method, a masking film formed by manual operation or by an apparatus for fabricating a pre-press masking film is used. The previously obtained negative film 6 and a film negative of the new photograph for replacement which is directly color separated by the scanner 4 are combined.
The correction carried out by using the apparatus for fabricating pre-press masking film will be described with reference to FIGS. 2 and 3. The coordinate data in association with the shape and position of the trimming frame of the image B.sub.0 on the negative film 6 are inputted to the conventional apparatus for fabricating a pre-press masking film. A portion of a color-dyed transparent film of a first masking film 7 is cut in accordance with the inputted coordinate data, thereby providing a masking portion M. The remaining portions of the color-dyed transparent film are peeled off and removed, leaving the masking portion M. A portion of the color-dyed transparent film of a second masking film 8 is cut in accordance with the shape and position of the trimming frame (generally the same as that of the image B.sub.0) of the image B.sub.0 ' of the new photograph B' (not shown) for replacement. The cut portion of the color-dyed transparent film is removed to provide a colorless transparent portion R.
The negative film 6 is laid over with the first masking film 7 to be corrected such that the image B.sub.0 which is to be replaced is in registration with the masking portion M. The film negative B.sub.n ' of the photograph B, (not shown) for replacement is laid over with the second masking film 8 such that the film negative B.sub.n ' is registered with the colorless transparent portion R. The images of the two sets of the overlapped films are combined on a positive film 9 by multiple exposure. The image B.sub.0 of the photograph B is replaced with the image B.sub.0 ' of the photograph B' (not shown) on the positive film 9. The above described operation is repeated four times to provide four color printing plates.
However, the above described prior art comprises some disadvantages. One of the disadvantages is that the corrected positive film is inferior in quality when the negative film is corrected by using a masking film fabricated in the conventional manner. The above described problem occurs more frequently especially when a negative film is to be corrected on which images edited by a layout system are exposed by means of a rotary cylinder scanner. The problem is due to the fact that when image data are arranged by the layout system and output and exposure are carried out by the scanner based on the arranged data, the formed images are tilted, though very slightly, in the subscanning direction.
More specifically, referring to FIG. 3, the shapes corresponding to the trimming frames of the images A.sub.0, B.sub.0 and C.sub.0 on the negative film 6 are designated as rectangles. However, the shapes corresponding to the trimming frames are actually formed to be parallelograms. One example is shown in FIG. 4.
Referring to FIG. 4, the trimming sides m.sub.1 and m.sub.2 of the image B.sub.0 on the negative film 6 are parallel to a subscanning direction X. However, the trimming sides m.sub.3 and m.sub.4 are not parallel to the main scanning direction Y. Namely, the trimming sides m.sub.3 and m.sub.4 are tilted by a small angle .theta. from the main scanning direction Y due to the scanning operation. It should be noted that the angle .theta. is considerably exaggerated in FIG. 4 for convenience. It is assumed that a position of a point on the trimming side m.sub.3 in the X direction changes by the length L.sub.X for the length L.sub.Y in the Y direction. Actually, the lengths L.sub.X and L.sub.Y are in the ratio 50 .mu.m:0.5 m=1:10,000. Namely, the tilt is very small which presents no problem in general, except in the case of the above described correction.
Meanwhile, in a conventional apparatus 10 for fabricating a pre-press masking film, a rectangular trimming area is usually designated by coordinate data which defines a rectangle. Consequently, the masking portion M and the colorless transparent portion R are formed to be rectangles, as shown in FIG. 5. Namely, the sides n.sub.1 and n.sub.2 of the masking portion M or the colorless transparent portion R are considered to be orthogonally intersecting with the sides n.sub.3 and n.sub.4. As a result, the problems occur on the corrected positive film 9. Namely, a very thin hairlike transparent portion remains unprinted along a side of the newly provided image B.sub.0 ' which is adjacent to the side n.sub.4. Sometimes, a hairlike thin line is generated at the boundary of images at the same portion as the images B.sub.0 ' and C.sub.0 are printed overlap each other. Consequently, the resulting printed material is inferior in quality.
The masking films can be manually fabricated in order to solve the above described problems. However, it is very difficult even for a highly skilled person to provide a highly precise masking film by manual operation. The manual fabrication requires much time and labor.
A method for fabricating a pre-press masking film to solve the above described problems is disclosed in Japanese Patent Publication Gazette No. 55136/1987, which method is of interest to the present invention. Generally, a block copy paper is reduced in size during the steps of pre-press process due to the influences of temperature and other factors. When the block copy is photographed, the images thereon are deformed due to the spherical aberration of the taking lens. Consequently, there will be differences in positions and scales between the masking portions or the colorless transparent portions formed on the masking film and the images formed on the positive film. The above mentioned method for fabricating a pre-press masking film is to cancel the above described differences. According to this method, the coordinate data representing the trimming frame designated by the layout system are corrected. The corrected coordinate data are transmitted to the common apparatus for fabricating a pre-press masking films. Consequently, a masking film having the masking portion or the colorless transparent portion transformed as desired can be provided. However, in the above mentioned publication, there is no disclosure of a preferable apparatus for realizing the above described method. There is a need for apparatuses capable of realizing the above described method.